A fundamental question of memory is whether the representations of different items are stored in localist/discrete or superimposed/overlapping manners. Neural evidence suggests that neocortical areas underlying visual object identification utilizesuperimposed representations that undergo continual adjustments, but there has been little corroborating behavioral evidence. We hypothesize that the representation of an object is strengthened, after it is identified, via small representational changes; this strengthening is responsible for repetition priming for that object, but it should also be responsible for antipriming of other objects that have representations superimposed with that of the primed object. Functional evidence for antipriming is reported in young adults, amnesic patients, and matched control participants, and neurocomputational models. The findings from patients dismiss explicit memory explanations, and the models fit the behavioral performance exceptionally well. Putative purposes of priming and comparisons with other theories are discussed. Priming and antipriming may reflect ongoing adjustments of superimposed representations in neocortex.